1 INTRODUCTION
Grassland covers approximately 40% of the Earth’s land surface (Pang et al., 2020b), and its multiple ecosystem services can sustain animal production, ecological functions, flora and fauna, and other human welfare (Costanza et al., 1997; Dong et al., 2020; Zhang et al., 2018). However, grassland ecosystem services have been demonstrated to be affected by herbivore disturbance (Lu et al., 2017; Martínez-Estévez et al., 2013).
Herbivore disturbance often has impacts on grassland ecosystem services (Lu et al., 2017) by altering the plant community (Lu et al., 2017; Niu et al., 2010; Wu et al., 2009) and soil properties (Lu et al., 2017; Sun et al., 2011; Wang et al., 2012a). Large herbivore grazing has been verified to influence grassland ecosystem services (Lu et al., 2017; McGranahan et al., 2012; Niu et al., 2010; Sun et al., 2011; Woldu and Saleem, 2000). In addition to large herbivores, tens of thousands of small burrowing herbivores usually create extensive disturbances on grassland vegetation and soil (Davidson et al., 2012; Pang et al., 2020a) by developing burrow systems (Sun et al., 2015), excreting feces and urine (Zhang et al., 2016), consuming plants (Liu et al., 2017; Sun et al., 2015), clipping tall plants (Zhang et al., 2020), and producing bare soil patches (Guo et al., 2012a, 2012b; Yu et al., 2017a, 2017b). Currently, a few studies have used data from one site to examine the effect of prairie dog disturbance on grassland ecosystem services in arid regions (Martínez-Estévez et al., 2013). However, the effect of disturbance by small burrowing herbivores on vegetation and soil varies with topography and microclimate (Pang et al., 2020a, 2020b; Wang et al., 2020a; Yu et al., 2017a). Therefore, it is necessary to use data from multiple sites to identify a general pattern concerning the effect of disturbance by small burrowing herbivores on grassland ecosystem services, which can provide information for grassland management.
Plateau pikas (Ochotona curzoniae ) are a common, small burrowing herbivore in alpine grasslands of the Qinghai-Tibetan Plateau (Smith & Foggin, 1999; Zhang et al., 2020). This small animal is considered a pest in China (Liu et al., 2013; Pang & Guo, 2017) since it often exacerbates alpine grassland degradation (Liu et al., 2013; Wilson & Smith, 2015; Zhang et al., 2016), and it has been widely eradicated by poison (Wilson & Smith, 2015). However, some studies argue that plateau pikas are key animals in alpine grassland ecosystems (Smith & Foggin, 1999; Smith et al., 2019). This kind of disagreement has encouraged professionals to reevaluate the role of plateau pikas in alpine grassland ecosystems. Thus, plateau pika disturbance in relation to alpine grassland ecosystem services is possibly a better way to gain insight into the roles of plateau pikas in alpine grassland ecosystems. In theory, alpine grasslands encompass a variety of ecosystem services, as well as grasslands in Europe (Jäger et al., 2020; Obermeier et al., 2019) and North America (Martínez-Estévez et al., 2013), whereas the main ecosystem services of alpine grasslands in the Qinghai-Tibetan Plateau are often given attention for forage availability, biodiversity conservation (Dong et al., 2010), water conservation (Dong et al., 2020; Wen et al., 2013), carbon sequestration (Dong et al., 2020; Zhang et al., 2015) and soil nutrient maintenance (Wen et al., 2013). However, whether plateau pika disturbance influences alpine grassland ecosystem services has not yet been well documented.
This study employs plateau pikas as a study animal to investigate the effect of disturbance by small burrowing herbivores on forage availability, biodiversity conservation, water conservation, carbon sequestration and soil nutrient maintenance services across five sites. Specifically, this study hypothesizes that (1) plateau pika disturbance is related to lower forage availability services and higher biodiversity conservation services; (2) plateau pika disturbance is associated with higher water conservation services; (3) plateau pika disturbance correlates with higher carbon sequestration services; and (4) plateau pika disturbance is related to lower soil nutrient maintenance services.